Chapter 7. Cell Interactions

Glycocalyx

A glycoprotein and glycolipid covering on the cell surface that provides protection, cell recognition, and signaling.

Extracellular Matrix (ECM)

A complex network of proteins and polysaccharides secreted by cells that provides structural and biochemical support to surrounding cells.

Basement Membrane

A specialized, dense ECM layer that separates epithelial and connective tissues.

Functions

Provides mechanical support, acts as a barrier, regulates cell behavior, influences cell differentiation, and serves as a filter in organs like the kidney.

Protein Components of the ECM

Collagens, fibronectins, proteoglycans, hyaluronic acid, glycosaminoglycans (GAGs), laminins.

Collagens

A family of fibrous proteins that provide tensile strength to tissues and are the most abundant proteins in the ECM.

Fibronectins

Glycoproteins that connect cells to the ECM, facilitate cell movement, wound healing, and help organize the ECM structure.

Proteoglycans

Heavily glycosylated proteins that attract water to provide hydration and resistance to compression in tissues; involved in cell signaling.

Hyaluronic Acid

A large, non-sulfated GAG that retains water, lubricates tissues, and is crucial for cell proliferation and migration.

Glycosaminoglycans (GAGs)

Polysaccharides that contribute to ECM hydration, cushioning, and cell signaling; include heparan sulfate, chondroitin sulfate, and hyaluronic acid.

Laminins

Adhesive glycoproteins found in the basement membrane that facilitate cell adhesion, differentiation, and migration by interacting with integrins and other ECM components.

Matrix Metalloproteinases (MMPs)

Enzymes that degrade ECM components to enable tissue remodeling, wound healing, and cell migration; regulated to prevent excessive degradation.

Integrins

Transmembrane receptors that link the ECM to the cytoskeleton, mediate signaling pathways, and regulate cell adhesion, migration, proliferation, and survival.

Focal Adhesions

Actin-linked cell-ECM attachment sites where integrins anchor the cytoskeleton to ECM proteins; involved in cell signaling and movement.

Hemidesmosomes

Specialized adhesive structures where integrins connect epithelial cells to the basement membrane via intermediate filaments, providing strong adhesion.

Selectins

Cell adhesion molecules that mediate transient, carbohydrate-dependent interactions between leukocytes and endothelial cells during immune responses.

IgSF Proteins (Immunoglobulin Superfamily)

Cell adhesion molecules that mediate interactions between immune cells and are involved in immune responses and neural development.

Cadherins

Calcium-dependent transmembrane proteins that mediate homophilic cell-cell adhesion and play a crucial role in maintaining tissue structure.

Adherens Junctions

Cell-cell junctions where cadherins connect to actin filaments, providing mechanical strength and facilitating signaling.

Gap Junctions

Channels formed by connexons that allow direct cytoplasmic exchange of ions and small molecules between adjacent cells for communication.

Tight Junctions

Seal cells together to prevent paracellular transport, maintain tissue polarity, and regulate selective permeability in epithelial and endothelial layers.

Desmosomes

Strong cell-cell junctions where cadherins connect to intermediate filaments, providing tensile strength and resisting mechanical stress in tissues like skin and heart muscle.

Human Perspectives Box Concepts

(Refer to the textbook for detailed examples related to human health and disease, including ECM-related disorders).

Junctions Forming the Blood-Brain Barrier

Tight junctions between endothelial cells in brain capillaries prevent the passage of most molecules, protecting the central nervous system.

Connexins

Protein subunits that form connexons, which assemble into gap junctions to facilitate intercellular communication.

Connexons

Hexameric protein structures composed of connexins that create channels for direct cell-to-cell exchange of ions and small molecules.

Tunneling Nanotubes (TNTs)

Long, thin, actin-based membranous channels that connect distant cells, allowing the transport of signaling molecules, proteins, and organelles.

Plasmodesmata

Cytoplasmic channels in plant cell walls that facilitate communication and transport of molecules between adjacent plant cells.